The present invention relates to a glow plug used to preheat a subcombustion or combustion chamber of a diesel engine, and more particularly, to an improvement in a better heating type glow plug with a rod heater having a plurality of projected heating fins mounted on the outer wall of the heating rod, designed to increase heating surface and dissipate heat to the air-fuel for achieving a fast heating function and improving heating characteristics.
Since a diesel engine generally has poor starting characteristics at low temperatures, a glow plug is mounted in a subcombustion or combustion chamber thereof. A current is supplied to the glow plug to heat it. The heat from the glow plug increases an intake temperature, or is used as an ignition source, so that the starting characteristics of the diesel engine are improved. A typical conventional glow plug is of a sheath type wherein a metal sheath is filled with a refractory insulating powder, and a coil heater of iron chromium, nickel or the like is embedded in the powder. Another typical conventional glow plug is of a ceramic heater type. The ceramic heater type glow plug has a rod heater prepared by embedding a heater wire of tungsten or the like in a ceramic material. Both types of the conventional glow plugs possess drawbacks and disadvantages the heating surface of the rod heater of the glow plug is not sufficient to preheat and ignite air-fuel mixture in the combustion chamber.
Turning to the starting characteristics of diesel engines, the greater a heating surface of a heating rod of a glow plug, the more easily or positively the engine can be started at low ambient temperature, particularly when the glow plug is comprising with heating fins dissipating heat into the combustion chamber. Namely, when the heating surface of the heating rod of the glow plug is small, it takes a long period of time from the initial explosion to the complete explosion. The heating fins are dissipating equally heat towards all directions in the combustion chamber, to accomplish a fast and smooth start of the engine.